Method and apparatus for obtaining an improved gravel pack

ABSTRACT

This specification discloses a process for providing a gravel pack adjacent a subsurface formation in a well having a string of casing therein. In carrying out this process, first perforations are formed through the casing adjacent the subsurface formation and materials are flowed therethrough to provide a consolidated gravel pack. Second perforations are thereafter formed through the casing to extend into and terminate within the consolidated gravel pack. Also disclosed is a well tool which may be employed in carrying out this process. This well tool is comprised in combination of an elongated body housing a means for forming perforations in casing in a well, which body has a recess in the lower end thereof. A plug is provided which is adapted to be set in the casing, which plug has fixed to the upper side thereof a protrusion that is adapted to be positively engaged by the recess.

United States Patent 1 Dismukes 51 Jan. 2, 1973 [54] METHOD ANDAPPARATUS FOR OBTAINING AN IMPROVED GRAVEL PACK [75] Inventor: Newton B.Dismukes, Dallas, Tex.

[73] Assignee: Mobil Oil Corporation 22 Filed: May 3, 1971 [21] Appl.No.: 139,525

[52] US. Cl. ..l66/276, 166/51, 166/297 [51] Int. Cl ..E21b 43/04, E2lb43/119 [58] Field of Search ..l66/5l, 276, 278, 280, 297; 175/4 [56]References Cited UNITED STATES PATENTS 2,652,117 9/1953 Arendt et a1...l66/278 3,404,735 10/1968 Young et al 3,483,926 12/1969 3,534,81610/1970 Showalter Primary Examiner-Marvin A. Champion AssistantExaminer-Jack E. Ebel Attorney-William J. Scherback, William D. Jackson,Henry L. Ehrlich, Andrew L. Gaboriault and Sidney A. Johnson '57ABSTRACT are flowed therethrough to provide a consolidated gravel pack.Second perforations are thereafter formed through the casing to extendinto and terminate within the consolidated gravel pack. Also disclosedis a well tool which may be employed in carrying out this process. Thiswell tool is comprised in combination of an elongated body housing ameans for forming perforations in casing in a well, which body has arecess in the lower end thereof. A plug is provided which is adaptedto'be set in the casing, which plug has fixed to the upper side thereofa protrusion that is adapted to be positively engaged by the recess.

6 Claims, 4 Drawing Figures PATENTEDJAM 2191s SHEET 1 OF 2 FIG.5

FIG. 2

FIG.!

' NEWTON B. DISMUKES INVEN TOR 542 ATTORNEY PATENTEDm 2:915 3.?08,013

sum 2 or 2 NEWTON B. DIS E5 INV OR TTORNEY METHOD AND APPARATUS FOROBTAINING AN IMPROVED GRAVEL PACK BACKGROUND OF THE INVENTION string ofcasing is normally run into the well and a ce- 0 ment slurry is flowedinto the annulus between the easing string and the wall of the well. Thecement slurry is allowed to set and form a cement sheath which bonds thestring of casing to the wall of the well. Perforations are providedthrough the casing and cement sheath adjacent the subsurface formation.

Fluids, such as oil or gas, are produced through these perforations intothe well. These produced fluids may carry entrained therein sand,particularly when the subsurface formation is an unconsolidatedformation. Produced sand is undesirable for many reasons. It is abrasiveto components found within the well, such as tubing, pumps, and valves,and must be removed from the produced fluids at the surface. Further,the produced sand may partially or completely clog the well, therebymaking necessary an expensive workover. In addition, the sand flowingfrom the subsurface formation may leave therein a cavity which mayresult in caving of the formation and collapse of the casing.

Various means including gravel packs have been used to control the flowof sand from subsurface formations. A particular type of gravel packoften used is a consolidated gravel pack. In forming such a pack,perforations are normally provided through the casing and cement sheathadjacent the producing formation. Fluid may be circulated through theseperforations to provide a cavity in the producingformation. Thereafter,granular material in a carrier solution is injected through theseperforations and packed tightly adjacent I packs are formedaboutperforated casing, the consolidated granular material forms apartial plug that fills the perforations formed through the cementsheath and the casing. This partial plug greatly reduces the fluidtransmission capacity of the perforations provided in p the casing andthereby reduces the total flow which can be realized from a producingformation through a fixed number of perforations.

SUMMARY OF THE INVENTION In accordance with an embodiment of thisinvention, a gravel pack is provided in a well adjacent a subsui faceformation, which well has a string of casing therein. In carrying outthe invention, first perforations are formed through the casing andmaterial is flowed through the first perforations to provide aconsolidated gravel pack adjacent the subsurface formation. Thereafter,second perforations are formed through the casing to extend into andterminate within the consolidated gravel pack.

In a preferred embodiment, the second perforations are of smaller sizethan the first perforations and are formed to extend through the firstperforations in the casing and to extend into and terminate within theconsolidated gravel pack.

In a further aspect of this invention there is provided a well toolwhich is particularly well suited for carrying out the process of thisinvention. This well tool is comprised in combination of an elongatedbody having therein means for forming perforations in casing and havingin the lower end thereof a recess adapted to positively engage aprotrusion; and a plug adapted to be set in the casing and having fixedto the upper side thereof a protrusion.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view whichillustrates a well that extends into an unconsolidated formation and hasa perforating tool oriented therein.

FIG. 2 is a schematic view which illustrates a consolidated gravel packformed adjacent the unconsolidated formation.

FIG. 3 is a schematic view which illustrates another embodiment of thisinvention.

FIG. 4 is a schematic view which illustrates a well having therein aperforation orientation plug and a perforation tool adapted to engagethe perforation orientation plug.

DESCRIPTION OF THE PREFERRED EMBODIMENTS This invention concerns amethod for controlling the production of sand from subsurfaceformations.

A well is drilled into the earth and into a subsurface formation such asan unconsolidated formation from which fluids are'to be produced. Astring of casing is run into the well and a cement slurry is injectedinto the annulus and allowed to set, thereby forming a cement sheathwhich bonds the string of casing to the wall of the well. Thereafter, incarrying out this method, first perforations or openings are formedthrough the casing and cement sheath adjacent the unconsolidatedformation, and material is flowed through these perforations to form aconsolidated gravel pack adjacent the unconsolidated formation. Thisconsolidated gravel pack extends into and partially plugs theperforations formed through the casing and cement sheath. Thereafter,second perforations or openings are formed through the casing and cementsheath, which second perforations extend into and terminate within thegravel pack.

Referring to FIG. 1, there is shown a well 1 extending into a subsurfaceunconsolidatedformation 3. A string of casing 5 is supported in the wellby a cement sheath 7. An orientation plug 9 having a protrusion such asan orientation wedge 10 fixed to the upper side thereof is positioned inwell 1 slightly below the portion of formation 3 to be perforated. Aperforating tool 11, having projectiles l4 and an orientation recess 13adapted to engage the orientation wedge 10, is positioned in the well 1such that the orientation recess 13 engages the orientation wedge 10.Perforating tool 11 is then fired,

forcing projectiles 14 into formation 3 and forming first perforationsl5. Thereafter, the perforating tool 11 is removed from the well and aconsolidated gravel pack is formed about the casing, as illustrated byconsolidated gravel pack 17 of FIG. 2. The perforating tool 11 is thenrerun into the well and second perforations 21 as illustrated in FIG. 3are formed to extend into and terminate within gravel pack 17.

It is desirable in the process of forming the consolidated gravel pack17 adjacent formation 3 that the formation 3 be washed through theperforations, thereby forming a cavity in formation 3 about casing 5.Thereafter, material such as granular material or particulated solids isinjected via a carrier solution through perforations 15, FIG. 2, andconsolidated to form consolidated gravel pack 17. A particular processby which the consolidated gravel pack 17 may be formed is described inU. S. Pat. No. 3,404,735. In accordance with this process, apredetermined amount of resin or consolidated fluid is dispersed in aquantity of an oilbase liquid hydrocarbon. Subsequently, a quantity ofparticulated solids is introduced into the resin-oil dispersion, thuscoating the solids with resin. The oilresin-solids mixture is thenintroduced into well 1 and injected through perforations 15 until asand-out or pack-out occurs and the desired amount of resincoated solidsis deposited in the well about casingv 5. Any excess solids are removedfrom the well by reverse circulating the solids out with limes or oil orby any other suitable means. An oil overflush-catalyst solution is theninjected through perforations 15. The catalyst solution cures the resinaround the packed solids and formation sand to cure or harden into ahardened, highly permeable sheath or mass capable of allowing productionof formation fluids free of formation solids. Particulated solids suchas those used in sand packing procedures in an amount of about one poundof solids per gallon are proportioned into the resin-oil mixture. A40-60 mesh (U.S. Sieve Series) sand or a mixture of 25 percent 4-8 meshsand and 75 percent 40-60 mesh sand is satisfactory. A service forforming such a pack is offered by l-Ialliburton Services, Incorporatedunder the trade name of Conpac and is described on page 2422, Volume 2,29th Revision of the COMPOSITE CATALOG OF OIL FIELD EQUIPMENT AND SER-VICES.

Referring to FIG. 4, there is shown a more detailed view of theorientation plug 9 and perforating tool 11 in well 1. The orientationplug 9 may be a bridge plug that is set on slips and that has anorientation protrusion 10 fixed to the upper side thereof. Theorientation protrusion 10 preferably is wedge-shaped, as shown, in orderto readily facilitate the positive engagement thereof by a correspondingorientation recess 13 provided in the lower end of perforating tool 11.The perforating tool 11 may be any of thewell-known means for formingperforations in casing such as means employing projectiles, for examplebullets or shaped charges. These projectiles are supported byperforating tool 11 such that they may be fired in a predetermineddirection with respect to perforating tool 11 through ports 12 andthereby form perforations in casing 5. Preferably these projectiles arearranged as illustrated by ports 12 to form perforations symmetricallyabout orientation recess 13. This enables first perforations to beformed in casing 5, perforating tool 11 to be disengaged fromorientation protrusion 10 and re-engaged therewith without regard toangular displacement and second perforations formed, which secondperforations coincide with the first perforations. It will be recognizedthat centralizers (not shown) or other means may be.

employed to centralize the tool 11 and thereby ensure that the tool 11is arranged at the same vertical angle each time it is engaged withorientation plug 9.

As shown in FIG. 2, consolidated gravel pack 17 extends into and fillsperforations 15 formed through cement sheath 7 and casing 5. Thisfilling of perforations 15 with consolidated gravel pack 17 greatlyreduces the well productivity over that which would be realized ifperforations 15 were free of granular material.

This reduction in well productivity is illustrated by considering atypical example which compares the well productivity when theperforations are filled with formation sand and with gravel. It iscustomary in perforating a well that a hole be formed having a diameterof one-half inch and a length of l to 1% inches through the casing andcement sheath. A perforation having these dimensions and filled with theformation sand which has an average permeability to oil of 800millidarcieswould transmit a maximum of about 1 barrel per day of 0.5centipoise liquid into the wellbore with a psi differential pressureacross the perforation. A l6,000-'millidarcy gravel would transmit about20 barrels per day under similar conditions. The usualpen forationdensity is about 4 shots per foot. Therefore, a production rate of from4 to barrels per day per foot would be obtained, depending upon whetherthe perforations are filled with formation sandor with injected gravel.Increasing the differentialpressure across the sand-filled orgravel-filled perforation hasprogressively less effect on oil-flow ratesince turbulent flow is established with higher differential pressuresand gas coming out of solution would reduce the permeability to oil ofthe material filling the perforations. Removal of the material fillingperforations 15 through casing 5 and cement sheath 7 would greatlyincrease the well productivity of the perforations over that possiblewhen the perforations are so filled.

In accordance with an embodiment of this invention, perforating gun 11is reloaded with a less powerful charge than was used in forming firstperforations l5 and with projectiles 19 which are of a smaller size thanprojectiles 14 that were used in forming perforations l5. Projectiles 19arepositioned in perforating gun 11 such that the center lines ofprojectiles l9 coincide with the former location of the center lines ofprojectiles l4. Perforating gun 11 is then fired, forming secondperforations 21 by forcing projectiles 19 through the gravel packmaterial filling perforations l5 and into the consolidated gravel pack17 where the travel of projectiles l9 terminates. The less powerful,

charge ensures that projectiles 19 will not penetrate throughconsolidated gravel pack 17 and into unconsolidated formation 3, thusensuring that the second perforations 21 terminate within consolidatedgravel pack 17. The smaller projectiles l9 enable the removal of theconsolidated gravel pack material filling the first perforations withoutundue shattering of the gravel pack.

As illustrated in FIGS. 2 and 3, the consolidated gravel pack 17 has thegreatest horizontal thickness opposite perforations 15. This is because,in forming a cavity in formation 3 and in forming the consolidatedgravel pack 17, material is injected through perforations where itimpacts upon formation 3 adjacent perforations 15. Further, in formingconsolidated gravel pack 17, there is a tendency for the granulatedmaterial to settle away from the upper extension of the cavity.Therefore, the horizontal thickness of consolidated gravel pack 17 maybe a minimum near the upper perforations 15.

In accordance with a preferred embodiment of this invention, perforatingtool 11 is loaded to fire projectiles 19 and form second perforations 21only in the lower portion of the consolidated gravel pack 17 leaving theuppermost perforations 15 partially plugged. This ensures thatprojectiles 19 do not extend through consolidated gravel pack 17 andinto unconsolidated formation 3.

It is recognized, of course, that the second perforations formed byprojectiles 19 could be formed through casing 5 and cement sheath 7 andinto consolidated gravel pack 17 at other locations than through theoriginal perforations 15. However, since the greatest horizontalthickness of consolidated gravel pack 17 exists about originalperforations 15, it is preferred that the perforating tool 11 be sooriented that projectiles 19 pass through the original perforations 15formed through casing 5 and cement sheath 7.

Another embodiment of this invention is illustrated in FIG. 3. Inaccordance with this embodiment, a packer 20 is set in casing 5 to sealupper perforations 15 This eliminates flow through those perforationsadjacent the portion of the gravel pack having the least horizontalthickness, thereby eliminating the possibility that unconsolidated sandsfrom formation 3 will be produced through these upper perforations intocasing 5. Thereafter, as illustrated by FIG. 3, second perforations 21are formed through the consolidated gravel pack material filling thelower perforations 15, which second perforations terminate within theconsolidated gravel pack 17. This opening of original lower perforations15 by second perforations 21 greatly increases the well productivity.

What is claimed is:

l. A method of providing a gravel pack in a well adjacent a subsurfaceformation, said well having a string of casing therein, comprising:

forming first perforations through said casing adjacent said subsurfaceformation;

flowing material through said first perforations to provide aconsolidated gravel pack adjacent said subsurface formation; and Iforming second perforations through said casing,

which second perforations extend into and terminate within saidconsolidated gravel pack.

2. The method of claim 1 further comprising sealing those firstperforations located adjacent the upper portion of said pack.

3. The method of claim 1 wherein said second perforations are formedthrough said first perforations in said casing.

4. The method of claim 3 wherein said second perforations are of asmaller size than said first perfora- 5 1% method of providing a gravelpack in a well adjacent a subsurface formation, said well having astring of easing therein, comprising:

positioning in said well a perforation orientation plug below said zoneto be perforated;

positioning in said well a perforation tool in engagement with saidperforation orientation plug; providing first perforations in saidcasing;

flowing material through said first perforations to provide aconsolidated gravel pack adjacent said subsurface formation;

repositioning in said well said perforation tool in engagement with saidperforation orientation plug; and

providing second perforations extending through said first perforationsand terminating within said consolidated gravel pack. 6. A method ofproviding in a well a gravel pack adjacent a subsurface formation, saidwell having a string of casing therein, comprising:

positioning in said well in fixed relationship to said casing a plughaving an orientation protrusion fixed thereto and extending upwardtherefrom;

positioning in said well a perforating tool having an orientation recessprovided in the lower portion thereof, said recess engaging saidorientation protrusion whereby said perforating tool is oriented in afixed position with respect to said casing;

forming first perforations through said casing;

withdrawing said perforating tool from said well;

flowing material through said first perforations to provide aconsolidated gravel pack adjacent said subsurface formation;

repositioning in said well said perforating tool and reorienting saidperforating tool in said fixed position with respect to said casing; and

forming second perforations which extend through said first perforationsin said casing and terminate within said consolidated gravel pack.

1. A method of providing a gravel pack in a well adjacent a subsurfaceformation, said well having a string of casing therein, comprising:forming first perforations through said casing adjacent said subsurfaceformation; flowing material through said first perforations to provide aconsolidated gravel pack adjacent said subsurface formation; and formingsecond perforations through said casing, which second perforationsextend into and terminate within said consolidated gravel pack.
 2. Themethod of claim 1 further comprising sealing those first perforationslocated adjacent the upper portion of said pack.
 3. The method of claim1 wherein said second perforations are formed through said firstperforations in said casing.
 4. The method of claim 3 wherein saidsecond perforations are of a smaller size than said first perforations.5. A method of providing a gravel pack in a well adjacent a subsurfaceformation, said well having a string of casing therein, comprising:positioning in said well a perforation orientation plug below said zoneto be perforated; positioning in said well a perforation tool inengagement with said perforation orientation plug; providing firstperforations in said casing; flowing material through said firstperforations to provide a consolidated gravel pack adjacent saidsubsurface formation; repositioning in said well said perforation toolin engagement with said perforation orientation plug; and providingsecond perforations extending through said first perforations andterminating within said consolidated gravel pack.
 6. A method ofproviding in a well a gravel pack adjacent a subsurface formation, saidwell having a string of casing therein, comprising: positioning in saidwell in fixed relationship to said casing a plug having an orientationprotrusion fixed thereto and extending upward therefrom; positioning insaid well a perforating tool having an orientation recess provided inthe lower portion thereof, said recess engaging said orientationprotrusion whereby said perforating tool is oriented in a fixed positionwith respect to said casing; forming first perforations through saidcasing; withdrawing said perforating tool from said well; flowingmaterial through said first perforations to provide a consolidatedgravel pack adjacent said subsurface formation; repositioning in saidwell said perforating tool and reorienting said perforating tool in saidfixed position with respect to said casing; and forming secondperforations which extend through said first perforations in said casingand terminate within said consolidated gravel pack.